Showing papers by "Hydro-Québec published in 1995"

AC flashover performance of insulators covered with artificial ice

Abstract: A field observation of ice accretion on Hydro-Quebec HV insulators was carried out, as well as a laboratory investigation of the AC flashover performance of various types of insulators covered with artificial ice. The field observations made it possible to identify the type and physical aspect of naturally occurring ice accretions produced during freezing rain precipitation. The laboratory investigation was conducted in a 4.8/spl times/2.8 m/spl times/3.8 m climate room using a HV transformer of 120 kV, 240 kVA with a short-circuit impedance of 5%. A method based on the standard IEC 507 method was developed for measuring the maximum withstand voltage (V/sub WS/) of ice-covered insulators. Various factors were investigated, including the effects on the insulator V/sub WS/ of such particulars as type, thickness, and uniformity of the ice, as well as the arcing distance of the insulators and the conductivity of freezing water. The effects of uniform ice, 2 cm thick, on 5 IEEE insulator units was thus considered to be equivalent to the effect of an ESDD of about 0.13 mg/cm/sup 2/ on the same insulators. >

Low-order black-box models for control system design in large power systems

Abstract: The paper studies two multi-input multi-output (MIMO) procedures for the identification of low-order state space models of power systems, by probing the network in open loop with low-energy pulses or random signals. Although such data may result from actual measurements, the development assumes simulated responses from a transient stability program, hence benefiting from the existing large base of stability models. While pulse data is processed using the eigensystem realization algorithm, the analysis of random responses is done by means of subspace identification methods. On a prototype Hydro-Quebec power system, including SVCs, DC power lines, series compensation, and more than 1100 buses, it is verified that the two approaches are equivalent only when strict requirements are imposed on the pulse length and magnitude. The 10th-order equivalent models derived by random-signal probing allow for effective tuning of decentralized power system stabilizers (PSSs) able to damp both local and very slow inter-area modes.

A two-factor saturation model for synchronous machines with multiple rotor circuits

Abstract: It is generally felt that no major accuracy breakthrough in predicting the steady-state and transient performance of synchronous machines could be achieved without taking proper account of the iron saturation effects as well as eddy-current losses. Although the two issues were often treated separately in the past, this paper attempts to unite them by developing a general model covering both the main-path magnetic saturation and frequency effects in the dynamic equations. Mathematical analysis in the d-q space pinpoints cross-saturation coupling which, a priori, does not seem to be symmetrical for salient-pole machines. Yet the model is theoretically sound, since it fulfils at least the physical constraints using energy balance principles. Some test points from a 555-MVA turbine-generator are used for an initial assessment the model's capability to predict the field current and internal angle for various loading conditions.

XPS investigation of surface oxidation and reduction in nanocrystalline CexLa1 − xO2 − y

Abstract: Inert gas condensation was used to generate nanocrystalline La-doped CeO 2-x . Non-stoichiometric CeO 2-x -based materials were found to he excellent catalysts in recent studies for the selective reduction of SO 2 . To understand better the stoichiometry-related catalytic properties, the surface chemistry of nanocrystalline La-doped CeO 2-x , was investigated through in situ oxidation-reduction thermal treatments. Oxidation in CO 2 and reduction in H 2 atmospheres were performed between 30 o C and 600 o C in a reaction chamber connected to an x-ray photoelectron spectrometer analytical chamber. Curve fitting and target factor analysis were used to obtain a semiquantitative measurement of the transformation between +3 and +4 oxidation states during these reactions. Target factor analysis was found to he a very useful tool for analyzing the contributions corresponding to Ce +3 and Ce +4

Neural network system using the multi-layer perceptron technique for the recognition of PD pulse shapes due to cavities and electrical trees

Abstract: A neural network system, utilizing the multi-layer perceptron approach has been applied to distinguish between power cable insulation partial discharge pulse shapes that are characteristic of cavities and electrical trees. The neural network was found to be capable of recognizing the differences in PD pulses produced by single cavity and electrical tree discharge sources. It also could differentiate between the discharge pulse forms emanating from electrical trees of different lengths; likewise, it was able to recognize changes in the shape of the discharge pulses with time due to aging effects. However, as these recognition capabilities relate only to comparisons of single discharge sources on a one-to-one basis, the application of neural networks to PD pulse shape recognition on actual power cables, where a number of different discharge sources may be discharging simultaneously, is quite premature at this time without more detailed exploratory work on complex discharge patterns. >

Book review: Knowledge-Based Systems Analysis and Design-A KADS Developer's Handbook by Stewart W. Tansley and Clive C. Hayball (Prentice Hall 1993)

Abstract: The acronym KADS (Knowledge Analysis and Design Support) has come to stand for a group of methods which can be applied to knowledge-based system development. KADS has become the de facto European standard and is being used with ever increasing frequency in North America as, for example, with the SOAR model [9]. As stated in the preface, the purpose of this book is to provide a full explanation of KADS plus a handbook for the use of KADS' methods. The authors' objective is to convince their target readers (practising computer professionals already well acquainted with the basic concepts of artificial intelligence) to adopt and use KADS. Note that although Prolog is the favored language in Europe, as well as that used by the developers of KADS, it is not used in this book, which simplifies the task of LISP users in applying the methods proposed.

Method of production of metal and ceramic powders by plasma atomization

Abstract: A metal or an alloy thereof, or a ceramic that has a liquid phase is introduced in the form of a rod or a wire or as a liquid stream into the apex formed by a plurality of converging plasma jets. Atomization takes place and upon controlled cooling good quality spheroidal powders are obtained whose size varies generally between about 10 and 300 μm.

Short circuit test performance of inductive high T/sub c/ superconducting fault current limiters

Abstract: The current limiting performance of inductive fault current limiters based on Bi-2212 high temperature superconducting tubes has been evaluated. Fault current limitation is due to the nonlinear impedance of this device when the induced current in the superconducting Bi-2212 tubes exceeds the critical current. A power load in a test circuit is first operated in nominal power conditions ( >

Effect of physico-chemical degradation of epoxy resin on partial discharge behavior

Abstract: Epoxy resin coated electrode specimens were subjected to partial discharges (PD) in air at twice the discharge inception voltage for durations ranging to 5000 h. The PD behavior was characterized by a transition from initially large pulse type discharges (- 200 to 300 pC) to either small pulse (- 1 pC), pseudoglow, glow discharge, or a combination thereof. Although these different forms of discharges were capable of occurring simultaneously, each type tended to prevail over certain periods of the exposure time. The physical and chemical nature of the degradation products formed on the surfaces of the epoxy resin also varied accordingly, indicating that each discrete form of discharge exerts its particular effect on the overall degradation process. Droplet formation on the central portion of the epoxy surfaces typified the large pulse discharge regime, whilst crystals formed within the transition region over which small discharge pulses (- 1 pC) were usually superimposed upon a continuous glow (pseudoglow and true glow regime). The droplets were identified as being partially comprised of a mixture of acids, mainly formic, glycolic, glyoxalic and nitric acids, whilst the crystals consisted of hydrated oxalic acid. Since similar results were obtained with discharges in both air and nitrogen, the effects of gas phase reactions on the PD activity would appear to be only of secondary importance compared to the reactions taking place on the surface of the epoxy resin. Since the test cell design did not allow any pressure variation within the discharge gap, the observed discharge transition cannot be attributed to pressure changes such as may take place within occluded cavities. Nevertheless, the transition observed here is similar to what is found with actual stator bar type insulation, suggesting that pronounced chemical and physical modifications on the surface of the physical cavity inclusions in the bar insulation may account for the characteristic PD behavior observed as a function of time.

Two‐stage electron acceleration by simultaneous stimulated Raman backward and forward scattering

Abstract: The coexistence of stimulated Raman forward and backward scattering of intense electromagnetic radiation, which can occur, for instance, in laser fusion plasmas, is investigated. The simultaneous Raman forward and backward scattering is shown to create an electrostatic field structure which is exceptionally efficient in producing highly relativistic electrons. The mechanism of the electron acceleration is analyzed both by Vlasov–Maxwell simulations with self‐consistent fields and by test particle calculations with prescribed electrostatic fields. The Vlasov–Maxwell simulations reveal that the two plasma waves generated by the backward and forward scattering are spatially separated, and thus form a two‐stage electron ‘‘accelerator.’’

Effect of overvoltage on the risetime and amplitude of PD pulses

Abstract: A two-dimensional mathematical model has been employed to characterize the pulse or spark breakdown behavior of a short gap in air. It has been established that the form or shape of a breakdown current pulse is very much determined by the overvoltage developed across the gap. Large overvoltages lead to intense space charge effects, which appreciably modify the breakdown current pulse form, leading to more rapid rise times, greater peak current amplitudes and reduced pulse widths. In so far as the overvoltage across a given cavity affects the rise time and amplitude of the pulse resulting from a spark type discharge, the response of a conventional partial discharge pulse detector is necessarily a function of the overvoltage developed across the cavity. >

Ionization and excitation behavior in a microcavity

Abstract: The excitation and ionization behavior of a 5 /spl mu/m cavity, subjected to an electric field of 270 kV/cm, has been examined. Data on the production of electrons, ions, dissociated molecules and excited species is presented and the associated charge transfer characteristics are considered. The implications of the ionization and excitation processes, as concerns their effect upon the degradation rate of solid insulation, are discussed. >

Case study on the integration of a non-utility induction generator to the Hydro-Quebec distribution network

Abstract: This paper investigates the influence of different factors (such as load and capacitive compensation levels, load and turbine dynamic behaviors, machine parameters) on induction generator self-excitation phenomena and related overvoltages, resulting from a fault and/or an unwanted network disconnection. Simulations are performed on a 25 kV distribution network related to an actual project of integration of a nonutility induction generator to the Hydro-Quebec power system. The paper presents the analysis of the results, as well as the derived guidelines for the determination of new relay settings and integration criteria for the Hydro-Quebec distribution network. >

A systematic method for power system restoration planning

Abstract: This paper describes a systematic method for power system restoration planning. System restoration at Hydro-Quebec is performed according to a set of detailed emergency instructions. The basis for these instructions is a restoration plan that is prepared off-line by operation planners. This plan includes a switching scenario with a set of values for the control variables-generator voltages, shunt reactors and load levels-that satisfy the operating constraints. Finding a suitable set of control variables usually requires many load-flow runs in a trial-and-error process. However, the problem can be formulated as a nonlinear optimization problem. The optimization algorithm which solves that problem provides values for the control variables automatically. This algorithm is linked to a user interface which constitutes a powerful tool for system restoration planning. >

Implementation of a new harmonic initialization method in the EMTP

Abstract: Nonlinear branches, such as saturable reactors, can generate harmonics and consequently increase the EMTP time-domain simulation time before the actual distorted steady-state is reached. This is an important initialization problem for transient analysis studies performed in steady-state operating conditions. This paper presents the implementation of a new method in the EMTP for initializing time-domain simulations. It is based on frequency domain steady-state calculations including harmonics from nonlinear branch functions. >

Experience with computer-aided graphical analysis of sudden-short-circuit oscillograms of large synchronous machines

Abstract: In a companion paper, computer programs are proposed for automating the analysis of sudden-short-circuit oscillograms in accordance with present IEC and IEEE standards. In this paper, we further illustrate the capabilities of computer-aided graphical methods with a view to their incorporation into modern testing practices. Using synthetic short-circuit data obtained from an exact solution of the network equations of known machines, it is first shown that use of the proposed software leads to satisfactory parameters in a number of realistic situations, including those where sub-subtransient effects are present. When faced with real data, it is shown that pre-filtering, without phase distortion, is often necessary and some useful tools are suggested for carrying this out. A thorough investigation of the automatic graphical method applied to three machines, differing widely in design, suggests that the new software is robust enough to be used on a regular basis, either in the field or in the design office. Using the Takeda & Adkins K-factor, derived graphically from the field current oscillogram, even a full second-order network is possible, matching the underlying phenomena, as seen from both the rotor and stator. >

Double-walled container for transporting and storing liquefied gas

Abstract: A double-walled container for transporting and storing a liquified gas or cryogenic liquid at low temperature. The container has an inner liquified gas holding vessel and an outer shell enclosing the inner vessel. The outer shell is coaxial with the vessel and of such a size as to provide a closed insulated space all around it. The inner vessel is suspended by its ends within the outer shell, with one end of the vessel being rigidly connected to the adjacent end of the shell while the other opposite end of the vessel is slidably connected to the other adjacent end of the shell so as to allow thermal expansion of the inner vessel and outer shell with respect to each other. Closable feeding and exit pipes pass through the outer shell and the inner vessel for introducing and draining the liquified gas into and off from the inner vessel. This container is light weight and can be of very great size; it can be used for the international transportation of liquid hydrogen by air, sea, rail or road.

Power distribution substation

Abstract: Disclosed is a power distribution substation for power distribution to a consumption pool having a high voltage unit divided into cells, each cell containing high voltage incoming connection equipments connected by high voltage cables to a power source having a voltage between 60 kV and 245 kV The substation also has a transformers yard having at least one transformer connected to the high voltage incoming connection equipments, and a mid-voltage unit containing outgoing connection equipments connected to the transformer and linked to output power lines for power distribution under a voltage lower than or equal to 36 kV Finally, the substation has a control room The high voltage and mid-voltage units, the transformers yard and the control room are located in a single building having a roof where the high voltage incoming connection equipments, the transformer(s) and some of the outgoing connection equipments ate located at the same level inside the building The substation includes an access passage that forms an integral part of the building The access passage is designed to insure direct access to the cells of the high voltage unit, the transformers yard and the mid-voltage unit The roof over the transformers yard has slats that may be opened and closed in order to allow cooling of the transformer(s) or recuperation of the heat generated by the transformer(s) whenever necessary Preferably, the outgoing connection equipments of the mid-voltage unit are of the self-relieving switchless type and incorporate a removable circuit breaker permutation system The substation is extremely compact, is of easy maintenance and is soundproof It is non-polluting as it may have an oil retention system This substation is thus particularly well adapted for urban use, while offering unlimited architectural designs

Deicing device for cable

Abstract: Disclosed is a deicing device for deicing cables. The deicing device includes one pair of conductive wires connected to and helically wound along the cable. The conductive wires are connected at one end to a pulsing device which generates an electromagnetic pulse within the wires, and are connected together at the other end. Upon a passage of the electromagnetic pulse in the wires, a repulsive force is created between the wires, which shakes the wires and shatters the ice that may be attached to the cable.

Method for mounting conductor sections onto a stator frame of a dynamoelectric machine

Abstract: A method for mounting conductor sections of a stator winding onto a circular shaped stator frame of a dynamoelectric machine. Each conductor section has two parallel conductor sides and at least one conductor head connecting two adjacent ends of the parallel sides. The stator frame is provided with circumferentially distributed parallel slots. One conductor side of each conductor section is inserted at least partially into a corresponding slot of the parallel slots. The other conductor side of each conductor section is positioned, one beside the other, along the stator frame. The other conductor sides are then circumferentially shifted with respect to the stator frame until the other conductor sides are superimposed respectively above the one conductor side for forming pairs of superimposed conductor sides. Thereafter, a force is applied onto the other conductor sides along a radial direction of the circular stator frame for inserting the pairs of superimposed conductor sides completely into the corresponding slots.

Analysis of in-service aged stator bars

Abstract: Stator bars subjected to operating stresses for 7 and 22 year periods were retrieved from a hydrogenerator to undergo short term electrical diagnostic tests in order to determine whether any significant aging of the insulation had taken place. The AC breakdown voltage (U/sub bk/), partial discharge inception voltage (PDIV), the maximum charge (/spl Delta/Q/sub m/) and total apparent charge (/spl Sigma//sub j//sup n//spl Delta/Q/sub j/) transfer of the partial discharges, tan/spl delta/ and tan/spl delta/ tip-up comprised the measured quantities statistically evaluated in the diagnostic test procedure. The AC breakdown voltage, PDIV and /spl Delta//spl theta//sub m/ were found to exhibit a systematic trend with in-service time, thereby suggesting the occurrence of aging effects. That is, both the AC breakdown voltage and the PDIV were characterized by a decrease with time in-service, whilst the /spl Delta/Q/sub m/ value exhibited an increase. However, no definite behavior was evinced by the (/spl Sigma//sub j//sup n//spl Delta/Q/sub j/), tan/spl delta/ and tan/spl delta/ tip-up values. The significance of the diagnostic test results is discussed in terms of Weibull statistics and the partial discharge behavior with time.

Impedance of multigrounded neutrals on rural distribution systems

Abstract: Hydro-Quebec has conducted field tests to study the impedance of multigrounded neutrals on rural distribution systems. Phase-to-neutral faults were staged at different locations along a 25 kV line and the field test results are reported. A simplified computer model implemented on EMTP gives results very close to those yielded by field tests. The main conclusion is that customers' grounding systems determine the impedance of multigrounded neutrals. Test results also show that the current is shared more or less equally between the neutral conductor and the sheaths of CATV and telephone cables. Overvoltages on phase conductors during phase-to-neutral faults were also measured and results are presented. >

A generalized harmonic balance method for EMTP initialization

Abstract: The harmonic balance method is extended to the steady-state analysis of power system models that include complex nonlinearities and variable topology power electronics equipment as may be user-assembled from basic EMTP-TACS components. In applying the harmonic balance method, these devices are considered as black boxes and isolated from the linear part of the model. A shooting method is used to accelerate the computation of their intermediate time-domain steady-state responses and to solve the harmonic balance equation formulated as a fixed point problem. Numerical tests show that the resulting generalized harmonic balance method is very promising for lightly damped dynamic power system models. >